1. Field of the Invention
This invention generally relates to document replication systems and, more particularly, to methods and systems for correcting color distortions.
2. Description of the Related Art
A scanner is a device that captures images printed on a medium such as paper and digitizes the image into a form a computer can use. Most scanners use charge-coupled device (CCD) arrays, which consist of tightly packed rows of light receptors that can detect the printed image in such a way that each element in the image is converted into an electrical charge, the intensity of which is related to a color in the color spectrum. In the scanning of printed images, the three color channels (red, green, and blue) may each suffer color distortions where both the green and blue channels are shifted with respect to the red channel. The color distortions may stem from the use of lesser quality blue CCDs in scanners, as compared to green or red CCDs, because people are less sensitive to blue than green and red. The color distortions may also arise from lens distortions as a result of temperature and humidity changes.
FIG. 1A is a simplified illustration of a scanner scanning a printed image. Scanner element 102 scans printed image 106 in the direction indicated by arrow 104. Scanner element 102 includes an array of CCDs that converts each element of printed image 106 to red, green, and blue pixel color values. As shown in FIG. 1A, printed image 106 includes five black squares along a row against a white background. As such, the scanned image is expected to be an exact duplicate of printed image 106 with only black and white colors.
However, as shown in FIG. 1B, actual scanned image 108 includes other colors in addition to black and white. The additional colors are the result of the above described color distortions. In particular, instead of being completely black, the edges of some squares are either slightly yellow or slightly blue. There are no color distortions in the center of scanned image 108 and, as a result, the center square is completely black. Nevertheless, on left side 110 of scanned image 108, the blue channel is shifted noticeably to the right, resulting in squares with blue left edges 114 and yellow right edges 116. In contrast, on right side 112 of scanned image 108, the blue channel is shifted noticeably to the left, resulting in squares with yellow left edges 118 and blue right edges 120.
In view of the foregoing, there is a need to provide methods and systems for correcting the color distortions in scanned images.